The present invention relates to a clamping device for a seat belt of a motor vehicle, the clamping device arresting the seat belt in response to a braking process.
German Published Patent Application No. 39 04 668 describes a passenger restraint system arranged in a motor vehicle. The passenger restraint system includes, in addition to airbags, seat belts, which are fitted out with a seat-belt tensioner . The seat belts together with the seat-belt tensioners assure that the vehicle passengers, in the event of accident, will be restrained in their seats, thus reducing the risk of injury.
German Published Patent Application No. 37 37 554 describes a triggering device for airbags and seat-belt tensioners, which is provided with a plurality of sensors, which react to a deformation and acceleration of the motor vehicle. In order that the decision regarding the triggering of a safety-device (airbag, seat-belt tensioner) be made as safely and reliably as possible, German Published Patent Application No. 37 37 554 provides that additional information regarding braking maneuvers be fed to the triggering processor and evaluated. This braking-maneuver information describes the kinetic behavior of the motor vehicle before and during an accident, from which the triggering processor derives control signals for the individual restraint systems in the motor vehicle.
According to the related art, the seat-belt tensioners are triggered together with the airbags. As a result of a braking maneuver that generally precedes the accident, the passengers, and this refers above all to the front-seat passenger, are tilted forward in the direction of the airbag unit. As experience has shown in the meantime, if the distance of the vehicle passengers to the airbag is too small, there is a great danger of injury once the airbag has been triggered.
PCT Publication No. 89/01430 describes a clamping device for a seat belt which is arrested in response to a heavy braking. In this context, from a cylinder an air pressure is built up which sets in motion a piston in opposition to a spring force, and due to the motion of the piston, a belt clamp outside the cylinder is locked via a lever system. However, this is a mechanically expensive arrangement.
An objective of the present invention includes providing a clamping device which has a compact design than can be realized with the least possible expense.
The present invention includes a clamping device with a cylinder in which a first piston and a second piston are movably supported. A seat belt is fed between the first position of the second piston through slots in a cylinder wall, at right angles to a cylinder axis. A force that is dependent on a brake pressure is exerted on the first piston, and a force in opposition to the brake pressure is directed at the second piston. Using the clamping device, a motor vehicle passenger is prevented, during a braking maneuver before an imminent collision, from bending in a direction of an airbag disposed in front of the motor vehicle passenger. The seat belt restrains the passenger, before the collision, in a position in which the triggering of an airbag is not dangerous for the passenger.
Thus, it is expedient that, in the event a first brake pressure threshold is exceeded, the clamping device grasps the seat belt tightly at its present extension length, and that, in the event a second brake pressure threshold that is higher than the first is exceeded, the clamping device tightens the seat belt.
The force exerted on the first piston can be exerted either by hydraulic or pneumatic means or by an electromagnetic actuator controlled by the brake pressure.